Effects of ambient pressure on flame spread speed along a fuel droplet array at microgravity

Microgravity experiments of flame spread along a fuel droplet array were performed to examine the effect of ambient pressure on the flame spread speed. The purpose of this research is to investigate growth mechanism of group combustion of fuel droplets. A fuel droplet array was suspended by SiC fibers of 14 μm in diameter. The number of fuel droplet was varied from 6 to 10 depending on the droplet spacing. Nondimensional droplet spacing and ambient pressure were varied from 2 to 12.5 and from 0.10 to 0.60 MPa, respectively. To simulate flame spread through a 3D fuel-droplet-matrix, a fuel droplet array was placed on the axis of a rectangular optical cell. n-decane was employed as a fuel. The normalized flame spread speed decreased as the ambient pressure increased. For all ambient pressures, the normalized flame spread speed takes the maximum between 3 and 3.75 in the nondimensional droplet spacing. The dependence of the normalized flame spread speed on ambient pressure increases with the increase in the nondimensional droplet spacing. An empirical model equation which expresses the dependence of flame spread speed on the ambient pressure was proposed.